The invention relates generally to photographic film cassettes and, more particularly, to a processing method and a fluid applicator including a pressure pad for use in slidably supporting incremental portions of a photographic film strip advancing in the film cassette, while avoiding particles carried by the film strip from becoming accumulated or trapped by and between the film strip and the pressure pad.
Multipurpose film cassettes have been developed for use in exposing, processing and projecting a strip of photographic film which is operated at all times in the cassette. Film cassettes of this type are disclosed in several U.S. patents assigned in common with the present invention.
In film cassettes of this category, a supply of light sensitive photographic film can be selectively exposed in a camera particularly adapted to receive and operate the cassette. To process or develop the exposed film, the cassette is removed from the camera and placed in a player or processing and viewing apparatus capable of activating a cassette contained processor for depositing a uniform layer of processing fluid on the film's exposed emulsion surface. During such processing a conventional series of successive, positive transparent images on the exposed film is developed. Following processing in the manner indicated, the player apparatus is operated as a projector. During projection, the film is incrementally advanced, frame-by-frame, past a light source. Accordingly, the series of positive transparent images of the scenes to which the film were exposed are capable of being successively viewed while projected onto a screen.
These cassettes have proven to be highly successful in operation. For successful operation, however, it is extremely critical that a uniform and extremely thin thickness of processing fluid be maintained over at least the exposed emulsion portion during film processing. Also, for successful operation, it is important to prevent the film's processed images from being adversely affected by objectionable processing fluid streaks or scratching. Towards the end of achieving the desirable thickness and eliminating undesirable fluid streaks, the cassette contains a spring biased pressure pad. The pressure pad supports the film strip in slidable engagement with a nozzle structure of the processor so that the film is in a predetermined spaced relationship to a doctoring surface of the nozzle, thereby facilitating formation of the desired thickness. In this regard, the film travels beneath the doctoring surface so that the latter forms the uniform processing fluid thickness; which fluid was earlier deposited onto the film strip through a nozzle opening positioned upstream of the doctoring surface in the context of film strip advancement during processing. To prevent film carried foreign particles from becoming trapped by the doctoring surface and thereby causing the objectionable streaks, the pressure pad has a leaf spring to provide a net balance of forces upon the film strip. In this manner, any foreign particles carried by the film's emulsion surface and trapped by the doctoring surface will cause a temporary increase in the spacing between the film and doctoring surface. Accordingly, particles which otherwise would be trapped can continue to be carried past the doctoring surface without causing the objectionable wakes or streaks.
The spring biased pressure pad is successful in avoiding having film carried particles trapped by the doctoring surface. A potential exists, however, for the wedging or trapping of foreign particles by the leading edges of the pad, which edges face in a direction opposite film strip advancement, and the film's nonemulsion surface during such advancement. This is because of the fact that not only are foreign particles carried by the film's nonemulsion surface, but also because the typical pressure pad is fabricated from metal and has the edges of the film engaging surface with curved corners which extend transversely across the film strip width. It will be appreciated that stamping of metal prevents formation of a film engaging surface having sharply defined or perpendicular corners relative to the remainder of the pressure pad. Rather, stamping causes formation of curved corners. Curved corners, or lack of perpendicularity of the film engaging surface corners, enables the film carried particles to become trapped by and between the leading edge corner of the film engaging surface, in the context of film strip advancement, and the film's non-emulsion surface. By reason of such trapping, there is the likelihood that such particles will scratch the non-emulsion surface.
Prior attempts to solve this scratching problem have suggested the use of a plastic pressure pad having film engaging surfaces with sharply defined corners to reduce the likelihood of film carried particles becoming trapped by and between the film and the pressure pad. Further, such film engaging surfaces have a width less than that of the film. This further reduces the likelihood of trapping. Despite such reduction, a potential for difficulties still arises by virtue of the fact that the leading edges of the film engaging surfaces create the potential for a certain amount of particle accumulation. Due to this trapping potential, there is a likelihood that the non-emulsion surface will be continuously scratched; thereby adversely affecting viewing of the processed film images.
Moreover, the problems of avoiding scratching of the non-emulsion surface are further compounded by the requirement that each cassette carry its own pressure pad and that the cassette and its components including the pressure pad must be capable of mass production manufacturing techniques and be within tolerance levels incident to such techniques for the system to be acceptable in a competitive commercial market. Accordingly, the structural organization of the means by which the film strip is supported in predetermined relationship to a cassette contained processor so as to avoid continuous scratching of the film's non-emulsion surface caused by trapped particles is critical to the overall system in which the cassette is used.